chapter_5_stereochemistry

Chapter_5_stereochem - Chapter 5 Stereochemistry The study of the 3-dimensional structure of molecules Stereoisomers have the same bonding sequence

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Chapter 5 Stereochemistry
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h The study of the 3-dimensional structure of molecules h Stereoisomers: have the same bonding sequence, but differ in the orientation of their atoms in space 191
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Chirality and Enantiomers (5-2) h Chiral objects : are those that have right-handed and left-handed forms The chirality of an object can be determined by looking at its mirror imag 192 image
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h A chiral object has a mirror image that is different from the original object (it is non-superimposable) Figure 5-1 193 Chiral Achiral : object that is not chiral
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Molecules can either be chiral or achiral Figure 5-6 Chiral compound Figure 5-7 Achiral compound 194
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A B Figure 5-3 195 In B : the original molecule and its mirror image are non- superimposable ( no plane of symmetry ) Chiral In A : the original molecule and its mirror image are superimposable ( plane of symmetry ) Achiral
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h Two molecules are said to be superimposable if they can be placed on top of each other and the 3-D position of each atom on one molecule coincides with the equivalent atom on the other molecule h Molecules that are non-superimposable 196 mirror images are called: Enantiomers
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Nomenclature of Asymmetric Carbon Atoms (5-3) h For a carbon atom to be chiral, it must have 4 different substituents . In this case the carbon atom is called: Figure 5-6 197 Chiral carbon Chiral centre Asymmetric carbon Stereocentre
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h Asymmetric carbons are marked with a * Figure 5-4 198
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h Generalizations If a compound has no chiral carbon , it is usually achiral If a compound has just one chiral 199 carbon , it is always chiral If a compound has more than one chiral carbon , it may or may not be chiral
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Rule of thumb: Any molecule that has an internal plane of symmetry cannot be chiral, even though it may contain chiral carbon atoms Figure 5-3 200
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h Because enantiomers are actually 2 distinct molecules with different properties, a notation (nomenclature) system for naming configurations of chiral carbon atoms was proposed by: Cahn Ingold Prelog 201 Cahn-Ingold-Prelog It assigns a letter ( R ) or ( S ) to the chiral carbon
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